This invention relates to measurement of the widths of stripes and spacings between stripes in a regular periodic pattern, and particularly to a reader for performing such measurements.
Although the present invention may be used to read the widths of many different types of regular periodic patterns, it hereinafter will be described with respect to reading the widths of opaque, light absorbing lines on a color picture tube faceplate panel of the matrix type before application of phosphor elements of a viewing screen.
Color picture tubes of the line screen matrix type have been commercially available for several years. The screens of such tubes comprise alternating lines of red, green and blue light-emitting phosphors, each separated from the other by light absorbing stripes called the matrix. In forming the tube screen, the matrix is applied first to the inner surface of a tube faceplate panel and then the phosphor lines are applied. The matrix and the phosphor lines are formed in a photographic process which uses the shadow mask of the tube as a photomaster. Each color-emitting set of phosphor elements requires a different light source location to ensure placement of the elements at locations that will be struck by electrons from an associated electron gun. Since the matrix is applied before the phosphor elements are applied, formation of the matrix requires three separate exposures to ensure that the holes in the matrix for the phosphors are in the proper locations. Because of this multiexposure method, the width of the matrix stripes and the spacing between stripes may vary from the ideal width and spacing desired. Since light output and color purity are at least partially dependent on the matrix stripe width and spacing, it is advantageous to determine this stripe width and spacing prior to completion of a screen.